The prior art describes various processes for the initiation of cationic polymerization, particularly the polymerization of epoxy materials. It is known to cure epoxy materials by use of curing additives such as polybasic anhydrides, organic peroxides, and quinone. It is further known that a metallocene, such as ferrocene, can be used as a curing accelerator for epoxy materials and is described in U.S. Pat. No. 3,705,129. U.S. Pat. Nos. 3,709,861 and 3,714,006 describe the use of cyclopentadienylmanganese tricarbonyl for the acceleration of the light-catalyzed reaction between polyepoxides and acid anhydrides or polymercaptans. U.S. Pat. No. 3,867,354 discloses the use of bis- and tris-salicylic acid complexes of chromium(III) to catalyze the reaction between epoxides and carboxylic acids, and U.S. Pat. No. 4,237,242 relates to the use of transition metal complexes (chromium, manganese, iron, etc.) of acetylacetonate type ligands to accelerate the thermally initiated reaction of carboxylic acid group-containing polymers with polyepoxides. Each of the above-mentioned patents teaches the acceleration of the reaction between polyepoxides and polyfunctional curing additives, but they do not teach the polymerization of epoxide group-containing compositions not containing a curing additive.
The polymerization of cationically-polymerizable materials, specifically epoxide group-containing materials, in the absence of curing additives is, however, well known. Among such processes are those in which the polymerization catalyst (also called sensitizer or initiator) is (1) a radiation-sensitive onium salt of a Lewis acid (e.g. diazonium salts as is described in U.S. Pat. No. 3,794,576 and U.S. Pat. No. 4,080,274; halonium salts as is disclosed in U.S. Pat. No. 4,026,705; and the onium salts of Group VIA elements, particularly the sulfonium salts, as are disclosed in U.S. Pat. No. 4,058,400); (2) a dicarbonyl chelate compound of a Group IIIA--VA element as is disclosed in U.S. Pat. No. 4,086,091; (3) a silver salt which is used for the polymerization of tetrahydrofuran as is described by Woodhouse, et al., J. Am. Chem. Soc. 100, 996 (1978); and (4) titanocene dichloride which is used for the polymerization of epichlorohydrin and 2-chloroethylvinyl ether as is described by Kaerijama et al., J. Polym. Sci., Chem. Ed. 10, 2833 (1972) and Ibid, 14, 1547 (1976). Compositions containing the above-mentioned catalysts are unsatisfactory because without the addition of optical sensitizers they are limited to ultraviolet radiation for polymerization. Furthermore, the dicarbonyl chelates are moisture sensitive and the titanocene dichloride requires a co-catalyst.